Atomically Precise Gold Nanoclusters: Synthesis and Catalytic Application - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 139

d n 9 r 4 n g | 3

Scheme 5.6 Homo-coupling of aryl iodides using Au 25 /CeO 2 catalyst.

the Ullmann-type homo-coupling reactions of aryl iodides. After optimiza-
tion, the suitable conditions for homocoupling reaction were as follows:
using DMF as solvent and K 2 CO 3 as base at 130 1C under a N 2 atmosphere.
Under such conditions, the Au 25 (SR) 18 /CeO 2 catalyst gave rise to 99.8%
conversion of iodobenzene (Scheme 5.6). The application of the Au 25 (SR) 18 -
catalyzed homo-coupling reaction was tested with substrates bearing a range
of substituents. The electron-rich substrates performed better than electron-
deficient substrates in the reaction. The support effect was also investigated,
but unlike the case of CO oxidation, no distinct effect of the oxide supports
was observed (i.e., CeO 2 , SiO 2 , TiO 2 , and Al 2 O 3 ).

.

5.5.4.2 Sonogashira Cross-coupling Reaction
Li et al. 26 expanded the catalytic application of the oxide-supported
Au 25 (SR) 18 nanocluster catalysts to the Sonogashira cross-coupling reaction
between iodobenzene and phenylacetylene. The supported catalyst was
made by impregnation of oxide powders (including CeO 2 ,TiO 2 , MgO, and
SiO 2 )inaCH 2 Cl 2 solution of Au 25 (SR) 18 ( 1 wt% loading), and then an-

nealed at 150 1C (1 h) in a vacuum oven. The supported gold particle size
after the annealing was confirmed by scanning transmission electron mi-
croscopy (STEM) to be identical with that of Au 25 , and thermogravimetric
analysis (TGA) confirmed that the protecting thiolate ligand remained on the
surface of gold nanoclusters after the annealing. The Au 25 (SR) 18 /oxide
catalysts after thermal treatment was applied in the Sonogashira cross-
coupling reaction between iodobenzene and phenylacetylene.

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